First post on bsky. We've updated our preprint about the change in the histone H3 variant on chromatin during Zygotic Genome Activation. Thanks to new experiments by Anusha, it seems like our initial, simplistic idea that the embryo "ran out" of H3 was not right. www.biorxiv.org/content/10.1... - ThreadSky

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aaamodeo.bsky.social • 76 days ago

First post on bsky. We've updated our preprint about the change in the histone H3 variant on chromatin during Zygotic Genome Activation. Thanks to new experiments by Anusha, it seems like our initial, simplistic idea that the embryo "ran out" of H3 was not right.

https://www.biorxiv.org/content/10.1101/2024.07.15.603602v2

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aaamodeo.bsky.social•76 days ago

We started out trying to explain why H3 goes up and H3.3 goes down on chromatin leading up to ZGA in the fly embryo. This is interesting because H3.3 is associated with both active transcription and heterochromatin which appear at ZGA.

aaamodeo.bsky.social•76 days ago

We made made H3/H3.3 chimeras and saw that chaperone binding sites were key. Also, H3/H3.3 chromatin levels depend on the local Nuclear to cytoplasmic ratio. But how do histones know the N/C ratio.

aaamodeo.bsky.social•76 days ago

In the first version of this paper we proposed that this was due to exhaustion of the (prefered) maternal H3 supply and that H3.3 was incorporated as a "second choice" H3. But when Anusha actually reduced the level of H3... H3.3 incorporation was unaffected!

aaamodeo.bsky.social•76 days ago

Next we thought that maybe H3.3 incorporation was downstream of transcription, but when she knocked down Zelda H3.3 was still incorporated just fine.

aaamodeo.bsky.social•76 days ago

Finally we used Chk1 to prevent cell cycle slowing and that did decrease H3.3 chromatin incorporation. BUT, it wasn't due to the cell cycle since H3.3 decrease precedes the change in cell cycle length!

aaamodeo.bsky.social•76 days ago

These results surprised us and have us thinking about zygotic chromatin composition in totally new ways! As always, biology is way more interesting and complicated than out overly simplistic initial explanations.

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